The present invention is related to a semiconductor package and its manufacturing method, and especially to a semiconductor package in which a semiconductor chip is attached to a lead frame and a method for manufacturing the same.
Currently, the structure of a semiconductor package, such as solid state image-sensing chip, photosensor, or ultraviolet erasable EP-ROM, includes a premolded resin block disposed ion the lead frame and having a concavity for exposing a portion of the lead frame in the resin molded block to allow the chip to be attached thereon and allow gold wires to be bonded thereon. After an image-sensing chip is directly attached to a predetermined position of the lead flame and electrically connected to the lead frame through gold wires, a covering member is bonded to the resin molded block so as to seal hermetically the whole concavity, thereby isolating the image-sensing chip and gold wires from outside. For example, U.S. Pat. No. 5,070,041 discloses such an image-sensing semiconductor package.
At the same time, in order to meet the requirement of a light, thin, and small electronic product with multiple functions, another chip with a different function is embedded in the above-described semiconductor package, as disclosed in U.S. Pat. No. 5,523,608. As shown in FIG. 8, U.S. Pat. No. 5,523,608 discloses a semiconductor package 1 having a chip 11 with peripheral pads attached on the bottom surface 100 of the lead frame 10. After the chip 11 is electrically connected to the lead frame 10 through gold wires 12, the lead frame 10 having a chip 11 attached thereon is placed in a package mold (not shown) to form a resin molded block 13 embedding the chip 11 and the gold wires 12 therein. When the resin molded block 13 is formed, a concavity 130 is formed on the top surface 101 of the lead frame 10 relative to the attaching position of the chip 11. The top surface 101 of the lead frame 10 is partially exposed in the concavity 130 so as to directly attach an image-sensing chip 14 to the lead frame 10 through the concavity 130. After the image-sensing chip 14 is electrically connected to the lead frame 10 through gold wires 15, a covering member 16 is bonded on the resin molded block 13 to seal hermetically the whole concavity 130 to accomplish a manufacturing method of the semiconductor package 1 with a multi-chip module.
In the above-described semiconductor package, the resin molded block with a concavity is molded and formed on the lead frame for attaching the semiconductor chip thereon to allow the image-sensing chip to attach on a surface of the lead frame exposed in the concavity. Because the flash of the resin is often formed on the surface of the lead frame exposed in the concavity during the molding process, it will affect the quality of subsequent die-bonding and wire-bonding processes, thereby decreasing the reliability of the fabricated product unless the flash is removed. Therefore, U.S. Pat. No. 5,070,041 discloses a method of removing flash from the semiconductor lead frame. First of all, an organic high molecular substance is coated on the predetermined surface of the lead flame exposed in the concavity of the resin molded block. After completing the molding process and forming the resin molded block partially embedding the lead frame therein, the lead frame combined with the resin molded block is placed in a solvent to remove the organic high molecular coating layer and then the die-bonding and wire-bonding processes are performed. However, such a method of immersing the lead frame combined with the resin molded block in the solvent which can dissolve the organic high molecular substance is time-consuming and complicated. Furthermore, the solvent containing the organic high molecular substance will result in an environmental pollution thereby increasing the processing cost.
U.S. Pat. No. 5,523,608 adopts a blasting way to remove the flash on the lead frame. Besides that the blasting way for removing the flash is time-consuming and requires an additional equipment thereby resulting in an increased cost, the flash particles separating from the surface of the lead flame will spray and adhere to the package equipment. If the flash particles cannot be effectively removed, they will influence the reliability of the next operation. Therefore, the package equipment must be also cleaned thereby further complicating the cleaning work. Moreover, during the blasting process, when a high-speed flow (gas or liquid) generated at a high pressure is applied to the lead frame, it will damage the resin molded block and lead frame, or even the chip with peripheral pads attached on the back side of the lead frame, thereby affecting the reliability of the fabricated product. In addition, this semiconductor package has two chips, and the heat generated from the chips cannot be effectively dissipated thereby influencing the useful life of the chip.
During the molding process of the above-described semiconductor package, the concavities in the upper mold and the lower mold of the used package mold are not symmetrical so that the resin flows for forming the resin molded block are respectively introduced into the concavities in the upper mold and the lower mold at different flow rates. It will easily cause the occurrence of void or popcorn. In addition, in the packaging process disclosed in U.S. Pat. No. 5,523,608, the resin flows respectively introduced into the concavities in the upper mold and the lower mold at different flow rates also easily result in wire sweep of gold wires bonded on the chip with peripheral pads disposed in the lower mold, such that short circuiting will likely occur due to the gold wires contacting each other.
An object of the present invention is to provide a method of removing flash from the semiconductor package, which can simplify the manufacturing process and decrease the manufacturing cost.
Another object of the present invention is to provide a semiconductor package and its manufacturing method which can enhance the heat-dissipating efficiency.
Yet another object of the present invention is to provide a semiconductor package and its manufacturing method which can prevent the occurrence of popcorn that can influence the reliability of products.
A further object of the present invention is to provide a semiconductor package and its manufacturing method without the problem of environmental pollution.
In accordance with one aspect of the present invention, the method includes the steps of preparing a lead frame having a first surface and a second surface, attaching an adhesive tape capable of being easily removed on the second surface of the lead frame, forming a resin molded block on a predetermined position of the first surface of the lead frame, removing the adhesive tape, attaching a semiconductor chip on a chip-adhering region of the second surface of the lead frame and electrically connecting the semiconductor chip with the lead frame, attaching a frame with a hollow portion on a predetermined position of the second surface of the lead frame by an adhesive agent and containing the semiconductor chip in the hollow portion, and bonding a covering member on the frame to seal the hollow portion for isolating the semiconductor chip from outside.
The method of the invention further includes steps after the step of attaching an adhesive tape on the second surface of the lead frame: attaching at least one semiconductor chip with peripheral pads to a predetermined position of the first surface of the lead frame, electrically connecting the at least one semiconductor chip with peripheral pads to the lead frame, and performing a molding process to form a resin molded block for covering the at least one semiconductor chip with peripheral pads. The semiconductor chip attached to the first surface of the lead frame can be a semiconductor chip with peripheral pads or a stacked structure having another semiconductor chip stacked on the semiconductor chip with peripheral pads. In the stacked structure, the semiconductor chip on the upper layer is electrically connected with the semiconductor chip on the lower layer through a solder bumps. Alternatively, the semiconductor chip on the upper layer is electrically connected with the semiconductor chip on the lower layer through gold wires, or is directly electrically connected with the semiconductor chip on the lower layer.
In the method of the present invention, because the second surface of the lead frame is attached by the adhesive tape 37, there is no resinous flash formed on the second surface of the lead frame during the molding process. After the adhesive tape is removed from the lead frame, the subsequent steps can be performed directly without requiring any additional cleaning step to remove the flash. At the same time, since the frame for containing the semiconductor chip in the hollow portion is premolded and then attached to the lead frame, the adhesion between the frame and the lead frame will not influence the connection between the semiconductor chip or conducting element and the lead frame. In addition, the frame is made of metallic material with a good thermal conductivity, such as copper, aluminum, copper alloy, aluminum alloy or the like, so that the heat generated by the semiconductor chip can be dissipated in the air. Thus, the semiconductor package of the present invention has a higher heat-dissipating efficiency. Moreover, because the resin molded block is only formed on the first surface of the lead frame, the problem of uneven flow rate of resin flow in the molding process can be prevented and no void is formed in the resin molded block.
In accordance with another aspect of the present invention, the semiconductor package includes a lead frame having a first surface and a second surface opposite to the first surface; a resin molded block formed on a predetermined position of the first surface of the lead frame; a frame attached to a predetermined position of the second surface of the lead frame by an adhesive agent and having a hollow portion for allowing a portion of the second surface of the lead frame exposed in the hollow portion to serve as a chip-adhering region; a semiconductor chip attached on the chip-adhering region and electrically connected with the lead frame; and a covering member bonded on the frame to seal the hollow portion for isolating the semiconductor chip from outside.